Provanna nakagawensis, Kaim & Jenkins & Hikida, 2009
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publication ID |
https://doi.org/ 10.4202/app.2009.0042 |
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persistent identifier |
https://treatment.plazi.org/id/03FBF625-FFC3-212E-7D7B-93DCFA8127C4 |
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treatment provided by |
Felipe |
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scientific name |
Provanna nakagawensis |
| status |
sp. nov. |
Provanna nakagawensis sp. nov.
Fig. 10 View Fig .
2008 Yasukawa provannid; Kaim et al. 2008a: 427, fig. 3D, E, I.
2008 Omagari provannid; Kaim et al. 2008a: 427, fig. 3F, J.
Etymology: After Nakagawa town, located close to the type locality.
Holotype: UMUT MM30178 View Materials , Fig. 10A View Fig , moderately preserved shell with no protoconch.
Type locality: Omagari site, Nakagawa area, northern Hokkaido, Japan. Coordinates 44 ° 39’26’’N, 144 ° 2’25’’E GoogleMaps .
Type horizon: Fossil hydrocarbon seep deposits of the Omagari Formation, Campanian, Upper Cretaceous.
Material.—76 moderately to poorly preserved specimens without protoconchs from the Omagari site and three poorly preserved specimens from the Yasukawa site.
Dimensions.—The holotype is 5.36 mm high and 3.35 mm wide.
Diagnosis.—Shell of small size, rather high, moderately inflated. Spiral ornament consists of two median prominent ribs and additional weaker rib adapically to the primary ribs. Spiral ribs intersected by orthocline axial ribs, which may fade away later in ontogeny. Blunt nodes present at intersections of spiral and axial ribs.
Description.—The shell is of small size, thin, melanoid to rissoid in shape with strong spiral and axial sculpture. In some specimens the axial sculpture is weak or absent. The protoconch is unknown. Spiral ribs are strong on juvenile whorls, two prominent ones and one weaker, which occur adapically of the other two. There might be an additional rib appearing abapically of the prominent ribs on some larger shells. The base is demarcated from the lateral flank by an additional strong spiral rib. The base is usually ornamented by 2–3 spiral ribs. Axial ribs orthocline, equally strong as spirals on the juvenile whorls and fading out on the adolescent whorls in some specimens. Aperture poorly preserved on the available specimens.
Discussion.—This thin−shelled species, although fairly common at the Omagari site, is usually poorly preserved. In this respect it is similar to many Recent species of Provanna . P. nakagawensis is most similar to Recent P. shinkaiae Okutani and Fujikura, 2002 from the Japan Trench. The latter species is also thin−shelled and ornamented by two prominent ribs but lacks the weaker adapical rib ( Okutani and Fujikura 2002). Moreover, P. shinkaiae has beaded or spiny intersections of spiral and axial ribs, while in P. nakagawensis blunt nodes appear there. Other similar species include P. pacifica (Dall, 1908) and P. goniata Warén and Bouchet, 1986 known from the eastern Pacific; both, however, are much larger than P. nakagawensis ( Warén and Bouchet 1986) . It is likely that one of the provannid shells (UMUT MM 29514) reported by Kiel et al. (2009: fig. 3E) from the Upper Cretaceous Akita Creek wood−fall association from Hokkaido belongs to P. nakagawensis . Also the provannid specimens reported by Kaim et al. (2008a) as “Gakkonosawa provannid” from Cretaceous Gakkonosawa seep carbonate may belong to P. nakagawensis .
Stratigraphic and geographic range.—Omagari and Yasukawa hydrocarbon seeps in Nakagawa area of northern Hokkaido, Japan. Campanian, Upper Cretaceous.
| UMUT |
University Museum, University of Tokyo |
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